The objectives of the study are to assess the effects on tests of intelligence and behavior of phenobarbital, a commonly prescribed anticonvulsant, in children. The design of this study permitted comparison of measures of tested intelligence and of behavior in children with febrile seizures who had been treated with phenobarbital, and in a group of seizure-free control children. A comparison of the groups allowed assessment of benefit and risk of treatment for a common childhood neurologic problem.